Two fundamentally different switching technologies exist that enable telecommunications. First, circuit-switching technology utilizes dedicated lines or channels to transmit data between two points, similar to public switched telephone networks (PSTN). The second, packet switching technology, utilizes a “virtual” channel to establish communications between two points. The virtual communication channel is shared by multiple communication processes simultaneously and is only utilized when data is to be transmitted. Since the differing performance requirements for voice transmission and data transmission impose different design priorities, historical development of voice communication systems such as the telephone, and its related business systems, such as a corporate business telephone system, e.g. Public Branch Exchange (PBX) and Automatic Call Distribution (ACD), has centered on circuit switching technology. Conversely, data communication systems, such as Local Area Networks (LANs), Wide Area Networks (WANs) and the Internet have primarily relied upon packet switching technology. As a result, separate cultures and networking fabrics have evolved for the design, development, application, and support for real-time voice communications, e.g. circuit switched networks, and non real-time data transmission, e.g. packetized data networks.
Because of the inherent differences in circuit-switched networked topologies and packetized network topologies, an apparatus know as a gateway is used to facilitate the exchange of signals and data between circuit-switched networks and packet-switched networks. Examples of such apparatus can be found in U.S. Pat. Nos. 6,282,193, and 6,631,238, both assigned to Sonus Networks, Inc. of Westford, Mass. Circuit-switched circuits operate in a synchronized manner and are typically switched from one Time Division Multiplexed (TDM) channel to another using a TDM switch to maintain synchronicity. Conversely, packetized networks, such as IP networks and ATM networks, operate in an asynchronous manner and are typically switched from one packetized channel to another with an asynchronous packet switch. As such, prior art gateways that facilitated switching within the synchronous domain and asynchronous domain, as well as cross-switching between the synchronous and asynchronous domains, required both a Time Division Multiplexed (TDM) switch for synchronous data and a packet switch for asynchronous data.
FIG. 1 illustrates a prior art gateway apparatus 100 that interconnects a circuit-switched network 202 and a packet-switched network 204 and facilitates the transmission of data within the packet-switched and circuit-switched domains, as well as across such domains. As shown, apparatus 100 comprises a packet switch 210, a time division multiplexed switch 112, packet integration logic 214, and a plurality of separate cards 205A-N each of which is capable of functioning as a source or destination of information associated with a time slot in the system. The TDM interface logic 219 of each card 205A-N is connected to circuit-switched network 202 by TDM Trunks 201. The TDM Trunks 201 represent implementations of standard telecom interfaces. TDM interface logic 219 comprises framers and mappers that may be used to implement various telecommunication protocols in a known manner and format data stream into virtual DS0 lines. The PAD logic 212 functions as packet adaptation logic which may be implemented with DSPs in a known manner. FIG. 1, TDM Highways 209 interconnect PAD logic 212 and TDM interface logic 219 with the Time Slot Interconnect (TSI) logic 213.
Time Slot Interchange logic 213 allows the serial data from one virtual DS0 line to be switched to another virtual DS0 line on a byte by byte level. Since a TDM data stream is a byte multiplexed synchronous serial data stream, the stream may be switched from one channel to another using the TDM switch 112 and the appropriate Time Slot Interconnect logic 213. If the TDM stream is to be converted to a packet destination, the Time Slot Interconnect logic 213 output is provided via another TDM highway 209 to a Packet Adaptation Layer (PAD) 212, which functions to build a packet from the DS0 data stream. The packetized data is then forwarded to the packet switch 210 within the gateway 100 after which it is then forwarded to a packet interface 214 and onto a destination within a packet network topology 204. Accordingly, prior art gateways require two switches, both a TDM switch 112 and a packet switch 212, to switch data between and among the circuit domain and the packet domain. Such dual switch architectures increase the costs of the apparatus.
FIG. 2 illustrates another prior art gateway apparatus 150, similar to apparatus 100 of FIG. 1, except that the Time Slot Interconnect logic 213 and the TDM switch 112 have been eliminated. As such, gateway 150 performs all switching asynchronously through the packet switch 212. Gateway apparatus 150 is simpler in design but is not capable of synchronous transmission of data. In FIG. 2, TDM Highways 209 connect DSPs used to implement PAD logic 212 directly to framers, and mappers used to implement TDM interface logic 219.
In addition, there exists protocols for streaming time sensitive data, such as audio and video communications. One such protocol is the IETF Real Time Protocol (RTP) which has a fixed delay between the source and the recipient, however, such delay is an unknown quantity. With an unknown fixed delay it is not possible to efficiently transport data through an asynchronous medium.
Various attempts have been made in the past to solve synchronization problems over wide area network through protocols that allow out of band distribution of information. One such protocol in described in U.S. Pat. No. 5,936,967, Baldwin et al., entitled “Multi-Channel Broadband Adaptation Processing,” and assigned to Lucent Technologies. Another such protocol, known as AAL1, is defined in published specifications entitled ITU-T I.363.1 “B-ISDN ATM Adaptation Layer specification: Type 1 AAL”, August, 1996; and ATM AAL1 Dynamic Bandwidth Circuit Emulation Service, AF-VTOA-0085.000, July, 1997. Revisions to the AAL1protocol, known as AAL2, is defined in published specifications entitled ITU-T I.363.2, ATM Adaptation Layer 2 (AAL2). The above-identified protocols, however, are intended for use with wide area applications and do not include synchronization information. Accordingly, these protocols are not suitable for internal synchronization of data across an asynchronous medium with a known constant and same delay.
Accordingly, a need exists for a gateway apparatus and protocol which is capable of efficiently switching data between and among the circuit domain and the packet domain.
A further a need exists for a gateway apparatus and protocol that is suitable for internal synchronization of data across an asynchronous medium with a known constant and same delay.
A further need exists for a gateway apparatus and protocol which is capable of efficiently switching data between and among the circuit domain and the packet domain.
A further need exists for a gateway apparatus and protocol which is capable of switching both asynchronous and synchronous data utilizing a single switch.
Yet another exists for a gateway apparatus and protocol in which all synchronous and asynchronous data is formatted using a common protocol to allow for efficient transport of the data with a fixed delay through an asynchronous medium.
Yet another exists for a gateway apparatus and protocol in which all synchronous and asynchronous data is formatted using a common protocol that allows of the data to be transported with synchronization information through an asynchronous medium.
Yet another need exists for a gateway apparatus which reduces the costs of the apparatus.